The present invention relates to the sterilization arts. It finds particular application in conjunction with hydrogen peroxide vapor systems used in connection with the sterilization of rooms, buildings, large enclosures, and bottling, packaging, and other production lines and will be described with particular reference thereto. It should be appreciated, however, that the invention is also applicable to other chemical vaporization systems such as those employing other peroxy compounds or aldehydes, for example, peracetic acid or formaldehyde vaporization systems.
Microbial decontamination of rooms and buildings can be achieved using chlorine dioxide gas. However, chlorine dioxide is highly toxic and must be recovered from the microbial decontamination process. Recovery of toxic gases from dilution air, leaking air, and the degassing of gas absorptive materials in the decontaminated room or building is difficult and time consuming. Further, care must be taken and monitors placed to insure that the toxic gas does not escape into the surrounding areas.
Sterile enclosures and other clean rooms are used by hospitals and laboratories for conducting tests in a microorganism-free environment. Further, a variety of medical, pharmaceutical, dental, and food packaging items are sterilized prior to use or reuse, in various forms of enclosures. Processing equipment for pharmaceuticals and food, freeze driers, meat processing equipment typically housed or moveable into large enclosures, or even rooms are advantageously sterilized.
Vaporized hydrogen peroxide is a particularly useful sterilant for these purposes because it is effective at low temperatures. Keeping the temperature of the enclosure near room temperature eliminates the potential for thermal degradation of associated equipment and items to be sterilized within the enclosure. In addition, hydrogen peroxide readily decomposes to water and oxygen, which, of course, are not harmful to the humans including technicians, people nearby, or people subsequently entering the treated space.
For optimally effective sterilization, the hydrogen peroxide is maintained in the vapor state. Sterilization efficiency is reduced by condensation. Several different methods have been developed for delivering a vapor phase sterilant to an enclosure or chamber for sterilizing the load (e.g., medical instruments) or interior thereof. In one option, the “deep vacuum” approach, a deep vacuum is used to pull liquid sterilant into a heated vaporizer. Once vaporized, the sterilant diffuses by its vapor pressure into an evacuated and sealed chamber. In another option, the “flow-through” approach, vaporized sterilant is vaporized in a flow of carrier gas, such as air, that serves to deliver the sterilant into, through, and out of the chamber, which may be at a slightly negative or positive pressure. A solution of about 35% hydrogen peroxide in water is injected into the vaporizer as fine droplets or mist through injection nozzles. The droplets fall on a flat heated surface which heats the droplets to form the vapor, without breaking it down to water and oxygen. A carrier gas is circulated over the heat transfer surface to absorb the peroxide vapor.
As the size of the enclosure increases, or the demand for hydrogen peroxide is increased, the efficiency of the vaporization system becomes more significant. The capacity of the vaporizer is limited in a number of ways. First, the vaporization process creates a pressure increase, reducing the flow of air through the vaporizer. This increases the sterilization time and effectively limits the size of the enclosure to one which is capable of sterilization within an acceptable time period. Second, to maintain sterilization efficiency, the pressure at which the vapor is generated is limited to that at which the hydrogen peroxide is stable in the vapor state.
One solution has been to increase the size of the vaporizer, the injection rate of hydrogen peroxide into the vaporizer, and the flow rate of carrier gas. However, the carrier gas tends to cool the heating surface, disrupting the vaporization process. Heating the heating surface to a higher temperature breaks down the peroxide.
Yet another solution is to use multiple vaporizers to feed a single enclosure. The vaporizers may each be controlled independently, to allow for variations in chamber characteristics. However, the use of multiple vaporizers adds to the cost of the system and requires careful monitoring to ensure that each vaporizer is performing with balanced efficiency.
The present invention provides a new and improved vaporization system and method which overcomes the above-referenced problems and others.